U.S. Pat. No. 4,461,286 issued to Sweat describes a percussive device operated by a trigger. It is capable of delivering a single impulse via a thrust pin, where the force of the impulse is stored in a spring. The spring and thrust pin are housed in a hand held device. The handheld device is positioned manually by a practitioner, both in location and direction. The location of the point of contact on the patient's body and the direction of the thrust are both important elements of the spinal and upper cervical impulse treatment device.
While Sweat offers some degree of control and repeatability in the impulse delivered to the body, it has several drawbacks. The force of the impulse is dependent on the energy held in the spring, as defined by Young's modulus, and this will drift over time, in a mechanical device like a spring, U.S. Pat. No. 4,841,955 issued to Evans uses solenoids and suggests means to improve accuracy and repeatability in impulse forces. In both of these hand held devices (HHDs), the precise angle of the thrust is determined manually, and may not be accurate or repeatable. Lastly, both Sweat and Evans are able to deliver only a single impulse and do not provide feedback on directional alignment.
U.S. Pat. No. 4,549,535 issued to Wing describes the generation of multiple impulses through use of an electric motor in combination with solenoids. Pulse width, frequency and amplitude are controlled, but the use of the motor and solenoids suggests some imprecision. The general waveform f(t) described in Wing has a square wave shape, with an undefined duty cycle, that is, time of impulse versus duration of resting. The device is hand held and directional alignment is not addressed.
U.S. Pat. No. 5,618,315 issued to Elliott describes delivery of multiple impacts in a linear direction, as well as applying rotational forces. Delivery is performed by a separate hand-held device (HHD), which provides visual feedback on direction alignment to the user. The HHD is managed by a separate controller device, including the user interface for input of impulse frequencies and modes, impulse energy, and HHD directional alignment angles.
The impulse waveforms disclosed in Elliott are specifically defined as square waves. This has more than one drawback. First, application of an abrupt force to sensitive parts of the body, like spinal vertebrae, is not desirable in spinal and upper cervical treatments. Further, a perfect square wave has infinite frequency components and is impossible to produce, in practice. Both electronic and mechanical systems which attempt to produce square waves will be driven to their performance limits, producing a waveform with overshoot on the rising and falling edges of pulses, followed by gradually decaying ringing, as seen in the bottom half of FIG. 4. Overshoot and ringing are high frequency artifacts, which/are viewed as undesirable in the intended application. If a square wave is filtered sufficiently to remove such artifacts and produce a smoother waveform, then it is no longer a square, wave by definition.
Both the abrupt nature of a square wave, and the high frequency artifacts described here, are seen as drawbacks in the application of an impulse device to spinal and upper cervical treatments.
Elliott has other drawbacks as well. The hand-held device (HHD) provides some visual feedback to a practitioner in terms of device positioning. The direction of the impulses to be delivered to the patient can be defined by two angles relative to vertical or by two direction vectors. These are input to the system on a separate, fixed controller unit, which may not be in the practitioner's direct field of vision during treatment. A set of light emitting diodes (LEDs) are placed in a cross-hair pattern on the top of the HHD, providing visual feedback to the user on the current angle of the device. Device positioning and directional alignment is done manually. A central LED lights up when a match to the preset direction vectors is achieved. At this time, the practitioner manually depresses a trigger to start impulse delivery.
The problems with this arrangement are subtle but significant. Even if the device is only moderately heavy, a practitioner may become mentally and physically fatigued after using it for several hours. The start of treatment depends on visual feedback and manual depression of a trigged. If the device moves out of alignment, there is no fail-safe mechanism. The visual feedback is a set of lights, not a set of direction vectors, which may or may not be preset correctly on a controller, and which are often outside the field of vision of the practitioner.
Some of these problems may be overcome by mounting the HHD on a fixed stand, an option mentioned by Elliott. Mounting the impulse device will reduce fatigue for the user and may also reduce the probability of misalignment during operation, but will not eliminate the potential for misalignment entirely. Elliott's impulse device has a rigid stylus and the stylus head is in contact with a sensitive part of the human body. Placement of the stylus head in a fixed location presents a new problem. Because the patient is also in a fixed location on a bed, a sudden movement by the patient can cause injury from contact with the stylus head. Therefore, the safety benefits gained from mounting the HHD on a fixed stand are counter-balanced by other safety problems introduced when creating a fixed location.
Elliott has some consideration for accuracy in its usage, but does not take a fail-safe approach, as just outlined. Efforts have not been made to eliminate all of the potential sources of human error during operation. In addition, the specification of a square wave as the impulse waveform is problematic, as explained above.
U.S. Pat. No. 6,228,042 issued to Dungan is similar to the device by Elliott, in that it enables the delivery of multiple impulses, at 30 Hz. Dungan's design continues to rely on components like solenoids or electric motors and is also a hand held device. Feedback on device alignment is not incorporated by Dungan, and for this reason the design is viewed as less effective than Elliott's.
U.S. Pat. No. 6,602,211 issued to Tucek also does not consider directional alignment. It uses a variable frequency controller and applies impulses through signals sent to electrical windings, which are analog in behavior and somewhat imprecise. Its primary feature is operational cut off when temperatures rise above an allowed setting. The latter feature is important for medical instruments used in the proximity of the body.
All devices discussed here have been hand held devices (HHDs), which generally lack precision in terms of the direction of delivery of impulses to the body for spinal and upper cervical treatment. Elliott is perhaps the best of these, since it offers some visual feedback on device direction. Operation is not fail-safe, however. Elliott also suggests mounting the device on a fixed stand, to reduce operator fatigue or directional inaccuracies, but a practical means of preventing patient injury from such a fixed device has not been considered.
Lastly, none of the devices described here have considered automation and data validation as an integral part of their design. Without comprehensive data validation, it is difficult to ensure safe, reliable and consistent instrument performance, as is highly desirable in spinal and upper cervical impulse treatments.